This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-328795, filed Nov. 18, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a thermal treatment method of heating or cooling a substrate such as, for example, an LCD substrate or a semiconductor wafer or the like, and a thermal treatment unit.
In processes of manufacturing semiconductor devices, the photolithography is performed on a surface of a substrate such as, for example, a semiconductor wafer (described as xe2x80x9ca waferxe2x80x9d hereinafter) or the like. In the photolithography, a sequence of processes are performed in which a predetermined pattern is exposed on the wafer after a resist solution is applied on the surface thereof and subsequently developing is performed thereon.
In such coating and developing processes, heat treatment is performed on the wafer if necessary after the resist coating, the exposing and the developing, and thereafter cooling processing is subsequently performed to cool the wafer in a state of a high temperature, to a certain degree.
A heat treatment unit for performing heat treatment has a heating plate in which a heater is embedded. The wafer is placed on the heating plate and subjected to heat treatment by heat from the heating plate. A temperature sensor is attached to the heating plate so that a temperature of the heating plate can be monitored. A signal from the temperature sensor is inputted to a controller for controlling a temperature of the heater based on the sensor signal sent from the sensor.
A cooling unit for performing cooling treatment has a cooling plate in which a Peltier element is embedded. The wafer at a high temperature after the heat treatment is placed on the cooling plate and subjected to cooling treatment by cold energy of the cooling plate. A temperature sensor is attached to also the cooling plate so that a controller controls a temperature of the Peltier element based on a signal from the temperature sensor similarly to the above-described heating plate.
Now, a state of the temperature of the heating plate when the wafer is heated up to a predetermined temperature is shown in FIG. 22. In a graph in FIG. 22, a horizontal axis indicates heating time [sec.] and a vertical axis indicates the temperature of the heating plate [xc2x0C.]. When the wafer is placed on the heating plate, the heating plate loses an amount of heat to the wafer and its temperature is lowered, as shown by Graph Line xe2x80x9ckxe2x80x9d in FIG. 22 (time t1 to t2 in FIG. 22). The controller, which recognizes the drop in temperature by the temperature sensor, increases an amount of electric power to the heater to start heat treatment. At this time, the temperature of the heating plate overshoots since heating by the heater is abruptly performed (time t2 to t3 in FIG. 22). Subsequently, the controller, which recognizes the overshoot by the temperature sensor, decreases the amount of electric power to the heater to lower the temperature of the heating plate (time t3 to t4 in FIG. 22). After passing through the processes as described above, the temperature of the heating plate becomes stable. Incidentally, PID control, in which a proportional element, an integral element, and a derivative element are added, is adopted for the controller so that excess properties can be improved by reducing a deviation to a minimum.
Next, a state of a change in temperature of the cooling plate when the wafer after the heat treatment is cooled to, for example, 23xc2x0 C. is shown in FIG. 23. In a graph in FIG. 23, a horizontal axis indicates cooling time [sec.] and a vertical axis indicates the temperature of the cooling plate [xc2x0 C.]. As shown by Graph Line xe2x80x9c1xe2x80x9d in FIG. 23, the temperature of the cooling plate maintains 23xc2x0 C. before the wafer is placed thereon. Then, when the wafer at a high temperature is placed on the cooling plate, the cooling plate receives an amount of heat from the wafer and the temperature of the cooling plate is raised (time t1 to t2 in FIG. 23). The controller, which recognizes the rise in temperature by the temperature sensor, subsequently increases an amount of electric power to the Peltier element to start cooling treatment. At this time, the temperature of the cooling plate undershoots 23xc2x0 C. since cooling by the Peltier element is abruptly performed (time t2 to t3 in FIG. 23). Thereafter, the controller, which recognizes the undershoot by the temperature sensor, decreases the amount of electric power supplied to the Peltier element to raise the temperature of the cooling plate (time t3 to t4 in FIG. 23). After passing through the processes as described above, the temperature of the cooling plate is stabilized to maintain 23xc2x0 C. Also in this case, PID control is adopted for the controller so that excess properties can be improved.
Incidentally, the wafer having a temperature of, for example, 23xc2x0 C. (a room temperature) undergoes heat treatment at 200xc2x0 C. in so-called prebaking (PREBAKE) for the sake of heating-removal of a resist solvent in a resist after resist coating, the wafer having a temperature of 23xc2x0 C. undergoes heat treatment at 90xc2x0 C. in post-exposure baking (PEB), and the wafer having a temperature of 23xc2x0 C. undergoes heat treatment at 30xc2x0 C. in postbaking (POSTBAKE) performed after developing treatment.
Conventionally, however, in spite of variations in heating temperatures under various heat treatments as described, one type of various data which are inputted to a proportional operation coefficient, integral time and derivative time among control parameters are used in PID control computed by a controller.
Therefore, although there is no particular problem when the wafer is heated to a specific temperature, when the wafer undergoes heat treatment at a temperature different from the specific temperature, a deviation is increased and excess properties are deteriorated since the controller cannot cope with the different temperature, thereby lengthening recovery time of the heating plate, more specifically, time which is required to stabilize the heating plate at a predetermined temperature. As a result, there is a risk of causing a reduction in a throughput.
In addition, there is a case where heating temperatures are different corresponding to recipes, for example, even in the same PEB, and also there is a risk that the recovery time is lengthened.
Similarly also in cooling treatment, various data inputted to control parameters are fixed to one pattern in PID control computed by a conventional controller. Therefore, although there is no particular problem when the wafer, which is heated to a specific temperature, is cooled to 23xc2x0 C., when the wafer, which is heated to a temperature different from the specific temperature, is placed on a cooling plate, the controller cannot cope with the different temperature, thereby lengthening recovery time of the cooling plate and causing a reduction in a throughput.
The present invention is made in view of the aforesaid points and its object is to shorten recovery time in heat treatment or cooling treatment.
In light of the above object, according to a first aspect of the present invention, a heat treatment unit of the present invention comprises a heating plate on which a substrate is placed, a heating element capable of heating the heating plate at different temperatures, a temperature controller which control a temperature of the heating element according to a transfer function, and a control parameter changing section which changes a setting of a control parameter in the transfer function at each of the different temperatures.
According to a second aspect of the present invention, a heat treatment unit of the present invention comprises a heating plate on which a substrate is placed, a heating element capable of heating the single heating plate at different temperatures, a temperature controller which controls a temperature of the heating element according to a transfer function represented by the following relational expression (1), and a control parameter changing section which changes at least any one setting of a proportional operation coefficient, integral time or derivative time among control parameters in the transfer function.
u=KP{e+(1/TI)xc2x7∫edt+TDxc2x7de/dt}xe2x80x83xe2x80x83(1) 
Therein, xe2x80x9cuxe2x80x9d expresses an amount of operation, xe2x80x9cexe2x80x9d expresses a deviation (a difference between a target temperature and a detected signal (an observed temperature)), KP expresses the proportional operation coefficient (a proportional gain), TI expresses the integral time and TD expresses the derivative time, respectively.
According to a third aspect of the present invention, a cooling unit which performs cooling treatment on a substrate of the present invention comprises a cooling plate on which the substrate is placed, a cooling temperature adjusting element which adjusts the cooling plate to a predetermined temperature, a temperature controller which controls a temperature of the cooling temperature adjusting element according to a transfer function, a temperature sensor attached to the cooling plate, and a control parameter changing section which changes a setting of a control parameter in the transfer function based on a temperature of the cooling plate detected by the temperature sensor after the substrate that is an object to be cooled is placed on the cooling plate.
According to a fourth aspect of the present invention, a cooling unit which subjects a substrate to cooling treatment comprises a cooling plate on which the substrate is placed, a cooling temperature adjusting element which adjusts the cooling plate to a predetermined temperature, a temperature controller which controls a temperature of the cooling temperature adjusting element according to a transfer function represented by the following relational expression (2), a temperature sensor attached to the cooling plate, and a control parameter changing unit which changes at least any one setting of a proportional operation coefficient, integral time or derivative time among control parameters in the transfer function based on a temperature of the cooling plate detected by the temperature sensor after the substrate that is an object to be cooled is placed on the cooling plate.
uxe2x80x2=KPxe2x80x2{exe2x80x2+(1/TIxe2x80x2)xc2x7∫exe2x80x2dt+TDxe2x80x2xc2x7dexe2x80x2/dt}xe2x80x83xe2x80x83(2) 
Therein, xe2x80x9cuxe2x80x2xe2x80x9d expresses an amount of operation, xe2x80x9cexe2x80x2xe2x80x9d expresses a deviation (a difference between a target temperature and a detected signal (an observed temperature)), KPxe2x80x2 expresses the proportional operation coefficient (a proportional gain), TIxe2x80x2 expresses the integral time and TDxe2x80x2 expresses the derivative time, respectively.
According to a fifth aspect of the present invention, a cooling treatment method of a substrate of the present invention comprises the step of changing a setting of a control parameter in a transfer function based on a peak temperature when a temperature of a cooling plate is raised by the substrate to reach the peak temperature on the occasion of placing the substrate on the cooling plate.
According to a sixth aspect of the present invention, a cooling treatment method of a substrate of the present invention comprises the steps of placing the substrate on a cooling plate, cooling the substrate to a predetermined temperature by controlling a temperature of the cooling plate according to a transfer function represented by the following relational expression (2), and changing at least any one setting of a proportional operation coefficient, integral time or derivative time among control parameters in the transfer function based on a peak temperature when the temperature of the cooling plate is raised by the substrate to reach the peak temperature on the occasion of placing the substrate on the cooling plate.
uxe2x80x2=KPxe2x80x2{exe2x80x2+(1/TIxe2x80x2)xc2x7∫exe2x80x2dt+TDxe2x80x2xc2x7dexe2x80x2/dt}xe2x80x83xe2x80x83(2) 
Therein, xe2x80x9cuxe2x80x2xe2x80x9d expresses an amount of operation, xe2x80x9cexe2x80x2xe2x80x9d expresses a deviation (a difference between a target temperature and a detected signal (an observed temperature)), KPxe2x80x2 expresses the proportional operation coefficient (a proportional gain), TIxe2x80x2 expresses the integral time and TDxe2x80x2 expresses the derivative time, respectively.
According to the heat treatment unit of the present invention, the settings of the control parameters in the transfer function are changed at every different temperature by the changing unit, whereby the temperature control means can properly perform the control corresponding to various heating temperatures. Accordingly, it is possible to improve excess properties and shorten recovery time regardless of the temperature when the heat treatment is performed on the substrate. Moreover, the stability of the temperature control is increased, whereby the substrate can be uniformly heated, resulting in the improvement of the uniformity of the surface portion thereof. Further, when PID control, in which even an integral element and a derivative element are added, is adopted for the temperature controller, a steady-state deviation (an offset) or thermal vibration is reduced, whereby the temperature control with higher precision can be performed.
According to the cooling unit of the present invention, the settings of the control parameters can be changed based on the temperature of the cooling plate detected by the temperature sensor after the substrate that is an object to be cooled is placed on the cooling plate, whereby the substrate can be efficiently cooled under the always appropriate control parameters even if its temperature is anything other than an assumed temperature. Therefore, recovery time can be more shortened than the conventional one. Additionally, it is possible to perform PID control by changing at least any one setting of a proportional operation coefficient, integral time or derivative time among control parameters based on the temperature of the cooling plate detected by the temperature sensor after the substrate that is the object to be cooled is placed on the cooling plate, so that the temperature controller, in which the settings of the respective control parameters are changed, can optimally control the temperature of the cooling temperature adjusting element.
According to the cooling treatment method of the present invention, the following effects can be obtained. For example, when the substrate after the heat treatment is placed on the cooling plate, the cooling plate receives an amount of heat from the substrate and its temperature is raised. Thereafter, the temperature of the cooling plate is raised to reach a peak temperature. Incidentally, if the relation between the peak temperature and an initial temperature of the substrate before the cooling treatment is inspected in advance by experiments or the like, it is possible to estimate the initial temperature of the substrate based on the peak temperature observed by the temperature sensor or the like provided on the cooling plate. Accordingly, the temperature of the cooling plate can be optimally controlled regardless of the temperature of the substrate when it is placed on the cooling plate. As a consequence, it is possible to improve excess properties and shorten recovery time regardless of the initial temperature of the substrate.
Additionally, according to the cooling treatment method of the present invention, a steady-state deviation (an offset) or the like is reduced and the temperature control with higher precision can be performed by further adopting PID control in which even an integral element and a derivative element are added in the transfer function.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.